Styrene oxide is used over a wide range of field, for example as a stabilizer for polymers, an ultraviolet ray absorber, a starting material in the preparation of drugs, a stabilizer for solvents, or as a starting material for phenethyl alcohol and phenethyl aldehyde which are useful as synthetic perfumes and sweetening materials.
For preparing styrene oxide by the epoxidation of styrene there generally is adopted a process in which styrene is epoxidised using an organic peracid. However, this process involves the following drawbacks and is not always satisfactory.                (1) During the reaction of oxidizing styrene with an organic peracid, the organic peracid is decomposed and there occurs an addition reaction of the resulting radical to styrene, thus resulting in that the selectivity of styrene oxide with respect to styrene is deteriorated.        (2) The resulting styrene oxide cleaves in the presence of an organic acid byproduced after the reaction, thereby producing an ester and a hydroxy compound, whereby the selectivity of styrene oxide with respect to styrene is deteriorated.        (3) Peracetic acid which is most easily available industrially among organic peracids is prepared by a so-called Daicel-Wacker process comprising air oxidation of acetaldehyde, but it is a very expensive oxidizing agent.        (4) In order to avoid a possible danger in the use of an organic peracid it is necessary to pay close attention to both operation and equipment.In order to overcome these limitations, the conventional route for epoxidation of alkenes is being attempted to be replaced by environmental friendly re-usable heterogeneous catalysts and hydrogen peroxide/molecular oxygen as oxidant.        
Y. W. Kobe in U.S. Pat. No. 3,806,467 (1974) proposed a process wherein an olefin and hydrogen peroxide are reacted in the presence of a bis(tri-n-methyltinoxy) molybdic acid catalyst to prepare an epoxide. However, as long as the working Examples thereof are reviewed, the yield of styrene oxide is a little lower than 3% (based on hydrogen peroxide) and thus this proposed process cannot be considered preferable as a styrene oxide preparing process. E. L. Lines et al. in U.S. Pat. No. 3,953,362 (1976) describes oxygen-containing molybdenum compound as catalysts for the epoxidation reaction of unsaturated organic compounds with peroxidic compounds such as hydrogen peroxide. In order to retard the co-production of undesirable organic compounds such as glycols, it is required to have no more than a minor amount of water present during oxidation. The main drawback of this invention is that the hydrogen peroxide using in the reaction must have less than 1 percent water in it.
E. L. Lines et al. in U.S. Pat. No. 4,157,346 (1979) describes an epoxidation method wherein an alkylene compound is reacted with a peroxidic compound, e.g., H2O2, in the presence of an improved molybdenum catalyst at 10 to 20 atmospheres pressure. The water which may be formed enhances the production of undesirable glycols, it desirable to maintain the amount of water to get epoxide selectivity. The main drawbacks of this invention are the high pressure required for the reaction and the contentious removal of the by-product water formed from the reaction mixture.
L. Kim in U.S. Pat. No. 4,418,203 (1983) describes a process for the epoxidation of olefins with hydrogen peroxide in a fluorinated alcoholic solvent using a catalyst selected from a group consisting of molybdenum, tungsten and rhenium and an organo metallic co-catalyst selected from the group consisting of organo tin, organo arsenic, organo antimony and organo germanium. The main drawback of this invention is the use of fluorinated alcoholic solvent for the reaction.
C. L. Hill in U.S. Pat. No. 4,864,041 (1989) A novel process for the homogenous oxidation of organic substrates is disclosed. This process uses a transition metal-substituted polyoxometalate catalyst, which in the presence of an oxygen donor, catalyses epoxidation reaction of the organic substrate. Typical oxygen donors used in this invention include C1-30 alkyl hydroperoxides, hydrogen peroxide, C6-30 iodosylarenes, C1-30 amine N-oxides, C1-30 peracids, hypochlorites, and other halogen oxyanions, oxaziridines, and highly oxidizing transition metal oxo compounds such as chromate, dichromate, permanganate, ruthenium and osmium tetroxides. The main drawback of this invention is the oxygen donor is required to use in equivalent to the amount of substrate or on a molar basis for the oxidation of the substrate.
P. R. Blum in U.S. Pat. No. 4,894,467 (1990) disclosed a process for making styrene oxide which comprises contacting styrene in the vapour phase with a molecular oxygen-containing gas over a silver metal catalyst containing a promoting amount of at least one alkali metal hydroxide selected from sodium, potassium and lithium hydroxides, on an inert solid inorganic support at contact times of from 0.6 to 10 seconds and temperatures from 200 to 350° C. The main drawback of this invention is that the reaction was carried out at vapour phase at high temperatures ranging from 200 to 350° C.
S. Enomoto et al. in U.S. Pat. No. 5,041,569 (1991) discloses a process for the styrene oxide preparation by reacting styrene and hydrogen peroxide in a heterogeneous system in the presence of a bis(tri-n-alkyltinoxy)molybdic acid and an amine such as ammonia, primary, secondary and tertiary methylamines, primary, secondary and tertiary ethylamines, primary, secondary and tertiary n-propylamines, primary, secondary and tertiary isopropylamines, primary, secondary and tertiary butylamines, primary, secondary and tertiary ethanolamines. The main drawback of this invention is that the process involves the use of amine promoters.
J. R. Monnier et al. in U.S. Pat. No. 5,145,968 (1992) disclosed a process for the selective monoepoxidation of styrene, styrene analogs, and styrene derivatives. Such compounds are contacted with an oxygen-containing gas in the presence of a promoted, supported silver catalyst at a pressure in the range of 0.1 up to 100 atmospheres, temperature in the range of 100 to 325° C. 0.5 to 75% conversion was obtained during the reaction. The main drawback of this invention is that the maximum conversion was only 75%.
K. Nishibe et al. in U.S. Pat. No. 5,155,241 (1992) describes a process for preparing Styrene oxide by reacting styrene and hydrogen peroxide in a heterogeneous system in the presence of a bis(tri-n-alkyltinoxy) molybdic acid catalyst and an inorganic anion as a promotor in the reaction. 62-77% conversion was observed and 45-100% selectivity was obtained. The main drawback of this invention is that the maximum conversion was only 77%.
K. B. Sharpless et al. in U.S. Pat. No. 5,939,568 (1999) discloses a rhenium-catalyzed epoxidation of olefinic substrates, accelerated by the accelerants having a nitrogenous aromatic heterocyclic structure. Use of the accelerants also enables the use of aqueous hydrogen peroxide as an oxidant. To achieve optimum acceleration, the accelerant should have a concentration within a range from 2.0 mole percent to 100 mole percent of the acclerant with respect to 1 mole of the olefinic substrate. The main drawback of this invention is that the process involves the use of 2.0 to 100 mole percent acclerants.
R. A. Grey et al. in U.S. Pat. No. 6,194,591 (2001) disclosed an olefin epoxidation process using a titanium zeolite catalyst modified with Pt, Pd, or Cu compound. The main drawback of this invention is that the titanium silicate zeolite catalysts are acidic in nature they also catalyse the epoxide isomerization and/or epoxide ring opening, thereby reducing the selectivity for the formation of epoxide in the epoxidation process over these catalysts.
B. Zhou et al. in U.S. Pat. No. 6,534,661 (2003) discloses a bimetallic, primarily Pt and Pd noble metals supported on titanium containing silica support for the epoxidation of organic compounds such as propylene using hydrogen and oxygen at elevated pressure of 500-2000 psig. In this disclosure, the presence of Pt, Pd and Ti is essential for the epoxidation to occur. In addition, the reaction is carried out in gas/liquid phase but at elevated pressures and the catalyst is prepared by impregnation of reduced Pd and Pt containing solution (by hydrogen) on the titanium containing zeolite support. After filtration of the impregnated mass and drying, it is further reduced in hydrogen at 250-300° C. for 10-20 hours. The main drawback of this invention is that the process of this disclosure is expensive and complicated requiring heterogeneous deposition for formation of the catalyst, and elevated pressures during application for epoxidation
V. R. Choudhary et al. in U.S. Pat. Publication No. 20050065355 (2005) discloses an invention relates to a process for the liquid phase epoxidation of a normally liquid olefinic compound to corresponding organic epoxide compound using aqueous or anhydrous organic hydroperoxide as an oxidizing agent in the presence of a supported nano-gold catalysts. The main drawback of this invention is that the process requires highly expensive nano-size gold particles as catalysts.
V. R. Choudhary et al. in U.S. Pat. Publication No. 20050113586 (2005) discloses an invention relates to a biphasic process for the epoxidation of an organic compound by organic hydroperoxide to the corresponding epoxide, using chromate or dichromate anions as the catalyst in aqueous medium. The main drawback of this invention is that the process requires organic hydroperoxide the mole ratio of 0.1 to 10 to olefinic compound.
Q. Tang, et al in Chem. Commun., 2004, 440-441 and Journal of Catalysis 230 (2005) 384-397, discloses the use of Co2+ containing molecular sieves as catalysts for the epoxidation of styrene with molecular oxygen. They observed a maximum styrene conversion 45% with styrene oxide selectivity 65%. The main drawback of their process is that the styrene conversion is only 45% and styrene oxide selectivity is only 65%.
J. Liang et al in Catalysis Communications, 2004, 5, 665-669, describes Fe2+-exchanged NaY zeolite and Fe2+-containing compounds including Fe3(PO4)2 and Fe3O4 as heterogeneous catalysts for the epoxidation of alkenes with molecular oxygen in the absence of a sacrificial reductant. A maximum styrene conversion 46.2% with styrene oxide selectivity 62.2% were observed in their reaction. The main drawback of their process is that styrene conversion is only 46.2% and styrene oxide selectivity is only 62.2%.